Chakravorty Sumeet, Groetsema Elizabeth, Obe Fatima Olayemi, Huntley Adam P, Anderson Gordon A, Clowers Brian H, Reilly Peter T A
Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.
GAA Custom Electronics LLC, Kennewick, Washington 99338, United States.
J Am Soc Mass Spectrom. 2024 Aug 7;35(8):1702-1712. doi: 10.1021/jasms.4c00110. Epub 2024 Jul 12.
Recent improvements to the comparison-based method of digital waveform generation increased the reproducibility of the waveforms so that the higher-order Mathieu stability zones can be accessed reliably. Digitally driven quadrupole mass filters access these zones using a fixed AC voltage and rectangular waveforms that are defined by a duty cycle. In this context, the duty cycle is the fraction of the waveform period where the waveform remains in the high state. Because digitally driven quadrupoles navigate stability using a duty cycle, there is no need to apply a resolving DC offset between electrode pairs. Accessing the higher stability zones using a conventional resonantly tuned RF requires the use of thousands of AC and DC voltages making the mode of operation less accessible with these devices. Stability zones higher than (1,1) and (2,1) have theoretical resolving powers that are on the order 1,140 and 3,447 at fwhm which drives efforts to practically access these operational conditions. Accessing these zones digitally requires the use of extremely precise waveforms. In a previous effort, waveform generation produced waveforms to reliably access the (1,1) and (2,1) zones without impacting performance. However, recent work found more improvement was needed to reliably access neighboring higher stability zones. Derived from that work, it was determined that a waveform resolution of ∼10 ppm or less was needed to reliably access the (3,1) and (3,2) zones. The present work utilized digital waveforms that achieve this level of precision to experimentally access and characterize attributes of the (3,1) and (3,2) zones. This work dives into the investigation of different beam energies to overcome the destabilizing fringing fields, improve transmission, and their overall effect on the experimental resolving power and signal-to-noise. In addition, the AC voltage of the driving RF was varied to understand the effects on the initial ion beam energy that is needed to achieve balanced separation and how the overall signal-to-noise is affected. Lastly, an assessment was made on the effects of the temporal parameters of a digital mass scan on peak sensitivity, peak fidelity, and overall duration for a scan.
基于比较的数字波形生成方法最近的改进提高了波形的可重复性，从而能够可靠地进入高阶马蒂厄稳定区。数字驱动的四极质量过滤器使用固定的交流电压和由占空比定义的矩形波形进入这些区域。在这种情况下，占空比是指波形处于高电平状态的时间占波形周期的比例。由于数字驱动的四极杆通过占空比来控制稳定性，因此无需在电极对之间施加解析直流偏移。使用传统的共振调谐射频进入更高的稳定区需要使用数千个交流和直流电压，这使得这些设备的操作模式难以实现。高于(1,1)和(2,1)的稳定区在半高宽处的理论分辨率分别约为1140和3447，这推动了人们努力实际进入这些操作条件。通过数字方式进入这些区域需要使用极其精确的波形。在之前的工作中，波形生成能够产生可靠进入(1,1)和(2,1)区域且不影响性能的波形。然而，最近的研究发现，要可靠进入相邻的更高稳定区还需要更多改进。基于该项工作，确定需要约10 ppm或更低的波形分辨率才能可靠进入(3,1)和(3,2)区域。本工作利用达到该精度水平的数字波形，通过实验进入并表征(3,1)和(3,2)区域的属性。这项工作深入研究了不同束流能量，以克服不稳定的边缘场、提高传输率以及它们对实验分辨率和信噪比的总体影响。此外，改变驱动射频的交流电压，以了解其对实现平衡分离所需的初始离子束能量的影响以及对整体信噪比的影响。最后，评估了数字质量扫描的时间参数对峰灵敏度、峰保真度和扫描总持续时间的影响。
